Mobile IP is standardized as an art for enabling continuous communication using the same IP address even when a mobile node moves among different networks (IP Mobility Support for IPv4, RFC3344, IETF 2002).
With the Mobile IP protocol, each time a mobile node moves to a different network, the location of the mobile node must be registered with a home agent, and the resulting processing delay has been an issue. As one method of resolving this issue, localized location registration, wherein mobility agents, which bear the functions of location management and data transfer, are hierarchized and movement within a narrow range is accommodated by registration with just an intermediate mobility agent, has been proposed (Mobile IPv4 Regional Registration, “draft-ietf-mobileip-reg-tunnel-07,” IETF 2002.).
FIG. 31 shows a network arrangement for carrying out localized registration. Foreign agents (FAs), which perform location management of mobile nodes (MNs) in a mobile network, are hierarchized by means of RFAs (Regional FAs) and GFAs (Gateway FAs), and when an MN moves inside the domain of an FA under an RFA or GFA, localized registration is carried out just in regard to the RFA or GFA.
With the conventional localized registration, since the FAs are hierarchized, a routing process is executed at each FA along the path before a packet reaches a mobile node within a mobile network, and this causes increased delay. There is also the issue that the higher the rank of an FA, the greater the number of mobile nodes that it must hold for path control.
FIG. 32 schematically shows the mobile node information that each FA must accommodate when the FAs are positioned hierarchically and shows that the higher the rank of an FA, the more mobile node information it must hold.
Here, in the case of the ordinary internet (fixed network), since the address system is managed so as to be coordinated with the connection system of the network, hierarchization consolidates the path information and is thus effective in terms of scalability.
On the other hand, with a mobile network in which nodes move about freely, since the address allocated to a mobile node is not necessarily coordinated with the address system of the network to which the mobile node is connected, scalability effects cannot be obtained by hierarchization. An upper-ranking FA must thus hold information of all mobile nodes under its domain, and this increases the processing load and has been a bottleneck in terms of scalability.
Also, with the mobile IP standard, the function of simultaneous bindings, with which the registrations of a plurality of addresses are held and data are transferred to these addresses, is defined in the home agent (HA). Thus for an MN to start communication at a destination, not only registration with the FA but registration with the HA must also be completed, and if registration with the HA is not completed, communication cannot be started even if registration with the FA is completed.
Furthermore with the mobile HP standard, packets to be sent to an MN are all sent to the HA regardless of the current location of the MN and since the packets are encapsulated at the HA for sending to the FA and then transferred, the packet transmission path becomes long inevitably and increased traffic is caused. In addition, since the encapsulation process at the HA and a decapsulation process at the receiving FA are required, the resulting delays cause lowering of the communication efficiency.
An object of this invention is to provide a mobile network and a communication method for the same, with which the processes for registration are simplified and the lowering of the data transfer rate is restrained by decreasing the number of mobile nodes for which each agent is to perform location management.
As with the present invention, since an IP packet transferred to the gateway GW from the external network is passed through all of the FAs regardless of its destination, the GW does not need to manage the accommodation location of each mobile node and does not have to execute a routing process. Also, since the routing process within the network is restricted to the FA that accommodates the mobile node, the processing speed is improved.